The present invention relates to wireless communication receivers, in particular to monolithically integrated receivers that are configurable for multi-carrier, multi-band operation.
Cellular technology is constantly evolving to support growing widespread wireless technology usage. Recently, popular wireless standardized technology has progressed from GSM (Global System for Mobile Communication) to WCDMA (Wideband Code Division Multiple Access) to LTE (Long Term Evolution). However, when a new wireless standard emerges, the previous standard version does not become obsolete because devices supporting the previous standard are still in use. In fact, two or more prior standard generation devices are typically still in circulation. Thus, wireless communication providers desire to support all standard generation devices that are in circulation concurrently.
In recent years, base station receivers capable of receiving multiple carriers with a single signal path have become commonplace. The advantage of these multi-carrier receivers is lower cost and smaller size as compared to a system made with receivers dedicated to each carrier.
Because different standards provide different signal characteristics, network equipment such as base station receivers have to be complex enough to support the different signal characteristics. Direct conversion receivers are emerging for WCDMA and LTE standards. Direct conversion refers to downconverting directly from radio frequency (RF) to baseband. While direct conversion eliminates circuit components, which lowers receiver costs, direct conversion also has drawbacks such as sensitivity to finite image rejection and harmonic distortion. WCDMA and LTE standard signals lend themselves for direct conversion because of their relatively low image-rejection requirement (˜70 dB). MC-GSM (Multi-Carrier GSM), on the other hand, has proved to be too difficult for direct conversion due to its large in-band blockers (−25 dBm in DCS/PCS bands and −16 dBM in GSM850/GSM900 bands) resulting in a ˜90 dB image rejection and harmonic distortion rejection requirement which isn't practical with known techniques.
Consequently, MC-GSM typically employs heterodyne conversion using intermediate frequency (IF) sampling. These conventional MC-GSM heterodyne receivers generally are not amenable to monolithic integration. For instance, IF filters and anti-aliasing filters used in heterodyne receivers typically require large inductors that are not practicable for silicon fabrication. In contrast, WCDMA and LTE receivers can use direct conversion receivers. The inability to support MC-GSM with a direct-conversion receiver prevents the development of a single platform that can support all standards.
Therefore, the inventors recognized a need in the art for a base station receiver that supports different standard signals, such as MC-GSM and WCDMA/LTE, with a single monolithic receiver.